At first i missed tempalte template arguments but then alias tempalte arguments should be their superset. But what am i doing wrong here:

import std.stdio;

template TypeList(T,U)
{
 struct TypeList
 {
  alias T Head;
  alias U Tail;
 }
}

class NullType{}
alias TypeList!(byte , TypeList!(short, NullType)) IntegerTypes;

template Length(T : NullType)
{
 //enum {value = 0 };
 const int value = 0;
}
template Length(alias TypeList)
{
 //enum {value = 1+Length!(TypeList.Tail).value };
 const int value = 1 + Length!(TypeList.Tail).value;
}

int main ( char [] [] args )
{
 writefln("Typelist length is %d",Length!(IntegerTypes).value);
 //writefln,getch;
 return 1;
}

The problem is in the Length template, if i use enums i get:
E:\D language\testtemplates\templates1\templates1.d(22): undefined
identifier template instance Length!(TypeList ).value
E:\D language\testtemplates\templates1\templates1.d(22): void has no value
E:\D language\testtemplates\templates1\templates1.d(22): incompatible types
for ((1) + (template instance Length!(TypeList ).value)): 'int' and 'void'
E:\D language\testtemplates\templates1\templates1.d(22): Integer constant
expression expected instead of 1 + template instance
Length!(TypeList ).value
E:\D language\testtemplates\templates1\templates1.d(28): template instance
Length!(TypeList ) error instantiating

and if i use const int i get:
E:\D language\testtemplates\templates1\templates1.d(23): non-constant
expression 1 + value

Can this be done in D?

Ivan Senji wrote:
> At first i missed tempalte template arguments but then alias
> tempalte arguments should be their superset. But what am i
> doing wrong here

It's because you're using "alias."  Change Length(alias TypeList) to Length(TypeList), though it would probably be less confusing to make it Length(T).


Sean

"Sean Kelly" <sean@f4.ca> wrote in message news:ckpqbl$2vkr$1@digitaldaemon.com...
> Ivan Senji wrote:
> > At first i missed tempalte template arguments but then alias tempalte arguments should be their superset. But what am i doing wrong here
>
> It's because you're using "alias."  Change Length(alias TypeList) to
> Length(TypeList), though it would probably be less confusing to make it
> Length(T).
>

Thanks a lot! I was sure i tried that but i didn't. Thanks :)

> Sean

Another question(hope this one is as easy to answer as the previous
one)

TypeList template is the same as in my firrst post:

//i think i got this one right
template IndexOf(X: NullType,T)
{
 enum{IndexOf=-1};
}

//but this specialization i don't know how to convert from C++:
template IndexOf(TypeList, T : TypeList.Head ) //templates1.d(41): no
property 'Head' for type 'TypeList'
{
 enum{IndexOf=0};
}

/*
in C++
template<class T, class Tail>
struct IndexOf<TypeList<T,Tail>,T>
{
 enum{value = 0};
};
*/

//this one is ok i think:
template IndexOf(TypeList,T)
{
 enum{temp = .IndexOf!(TypeList.Tail,T)};
 enum{IndexOf = temp ==-1?-1:1+temp};
}

Hope someone can answer :)